Very long storage causes deterioration in aluminium oxide layer of electrolytic capacitors.
(normal leakage current during use constantly rebuilds oxide layer)
So there's risk that it won't work fully at first with capacitors not functioning fully.
With worst case being that some capacitors are shorted, or leakage current unsafe.
Would myself first check with oscilloscope that 5V standby is correct and ripple is in specs.
After that would jump start it and measure other rails.
Certainly would run it some without anything valuable connected.
